28 lines
951 B
Plaintext
28 lines
951 B
Plaintext
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:- module(topsort, [topsort/2]).
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:- use_module(library(ordsets),
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[ord_subtract/3]).
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/* simple implementation of a topological sorting algorithm */
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/* graph is as Node-[Parents] */
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topsort([], []) :- !.
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topsort(Graph0,Sorted) :-
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add_parentless(Graph0, Sorted, IncludedI, Graph1, SortedRest),
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sort(IncludedI, Included),
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delete_parents(Graph1, Included, NoParents),
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topsort(NoParents, SortedRest).
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add_parentless([], Sorted, [], [], Sorted).
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add_parentless([Node-[]|Graph0], [Node|Sorted], [Node|Included], Graph1, SortedRest) :- !,
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add_parentless(Graph0, Sorted, Included, Graph1, SortedRest).
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add_parentless([Node|Graph0], Sorted, Included, [Node|Graph1], SortedRest) :-
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add_parentless(Graph0, Sorted, Included, Graph1, SortedRest).
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delete_parents([], _, []).
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delete_parents([Node-Parents|Graph1], Included, [Node-NewParents|NoParents]) :-
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ord_subtract(Parents, Included, NewParents),
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delete_parents(Graph1, Included, NoParents).
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